math/abacus: unbreak build on 11.0C [1] and fix minor issues
- Builds fine with gcc42 and clang
- Build shared library versioned (for soname in future)
- Fix LICENSE
- Improve style of post-patch target
- Convert to NO_WRKSUBDIR
- Convert to INSTALL_LIB
- Parenthesize commands using cd
- Wrap long lines
PR: 199243
Submitted by: tkato432@yahoo.com
Reported by: pkg-fallout [1]